1. Field of the Invention
The present invention relates to an optical sweep signal generator which is applicable to the fields of the optical communication, optical information processing, optical instrumentation and the like.
2. Prior Art
In the fields of the optical communication and optical instrumentation, the optical sweep signal generator is used to effect a sweep on the oscillating optical frequency of the laser or the like. And, many attempts are made to develop technology for the optical sweep signal generator.
The variable-wavelength semiconductor laser is designed to vary the oscillating optical frequency. In general, the oscillating optical frequency of the semiconductor laser has a property of non-linear variation to the electric current and voltage, which are used to control the oscillating optical frequency, as well as a property of non-linear variation to the temperature. Such properties of non-linear variation may deteriorate quality in communications or they may cause incorrectness in the optical instrumentation. In order to avoid such disadvantages, it is necessary to effect a sweep on the oscillating optical frequency in such a way that the oscillating optical frequency is varied linearly with respect to time.
In order to vary the oscillating optical frequency linearly with respect to time, it is not necessary to alter the electric current and voltage, which control the oscillating optical frequency, at a constant rate; and it is not necessary to alter the temperature at a constant rate. Instead, the conventional technology performs a so-called `assumed control` so as to provide the oscillating optical frequency which is varied linearly with respect to time. Specifically, a relationship between the oscillating optical frequency and its control signal is examined in advance; and then, the control signal is controlled in such a way that the oscillating optical frequency is varied linearly with respect to time.
However, due to the disturbance such as the variation of temperature and due to the time-elapsed change in properties of the circuit elements of the conventional technology, the relationship between the oscillating optical frequency and its control signal should be changed. Therefore, the conventional technology suffers from a problem that the above-mentioned factors deteriorate the linearity in variation of the oscillating optical frequency with respect to time.